1. Field of the Invention
The present invention relates to an atomising nozzle and to such a nozzle with a filter, notably to one which produces a spray of fine droplets suitable, for example, for the administration of a medicament by inhalation, to the production of such nozzles, and to a spray-generating device incorporating such nozzles.
2. Description of the Prior Art
It is known (e.g. from WO 91/14468) that fluids can be caused to form very fine droplets on being forced through narrow nozzles at high pressure. WO 91/14468 proposes to manufacture the necessary nozzles using methods such as those known in the manufacture of spinning nozzles. These nozzles are produced, for example, by boring through a thin metal plate with a tungsten-carbide. An important area of application for the equipment according to WO 91/14468 is the production of aerosols for inhalation therapy. Demanding requirements are imposed among other things, on the fineness of the droplets; it has been found during numerous investigations that a considerable number of droplets must have a size less than 6 xcexcm in order that a sufficient quantity of the medicine can reach deep enough into the lungs. For safe treatment the individual pieces of equipment must each produce the same droplet spectra, since only then is it certain that the given dose of the medicine will be delivered to the lungs in the desired way.
With the mechanical production of nozzles there are sometimes disturbing deviations from nozzle to nozzle, possibly due to the walls of the nozzles being of varying degrees of roughness. It is, amongst other things, difficult to produce double nozzles, like those shown in FIG. 8 of the afore-mentioned WO 91/14468, with the necessary accuracy. In addition, it is not an easy matter to obtain nozzles of changing cross-section using known methods. possibly with a view to accelerating or slowing down the flow of fluid in the nozzle, or to provide impact elements or vortex-generating devices.
In PCT Application No GB91/00433, there have been described methods and devices for forming sprays of fine droplets from a fluid without the use of pressurised propellant gasses, notably for the formation of sprays of a fluid medicament which have a mean droplet size of less than 10 micrometres for inhalation by a user so that the droplets of medicament can penetrate into the lower lung. In PCT Application No GB91/02145, there have been described methods and devices by which the formation of such sprays can be optimised by inducing secondary flows in the stream of fluid when it passes through the nozzle aperture.
In the preferred form of such methods and devices, a metered dose of the fluid medicament is drawn from a reservoir into a pressure chamber by retracting a piston in a cylinder of a pump mechanism against the action of a drive spring. The piston or spring is latched or otherwise retained in the retracted, or cocked, position so that the metered dose is held at ambient pressure in the pressure chamber of the pump until it is discharged. When discharge is required, the piston or spring is released and the spring drives the piston forward, thus applying a rapid pressure rise to the fluid causing it to discharge through the nozzle aperture and form a spray of droplets.
The very fine droplets required for the application of a medicament to the lower lung are achieved by the use of fine aperture size nozzles and high pressures, typically with nozzle apertures of less than 20 micrometres and pressures in excess of 300 bar.
The nozzle apertures required to achieve such fine droplets can be formed in a number of ways, for example by punching a hole in a metal plate and part closing up the hole to achieve a fine aperture with a rough rim which causes the secondary flows in the fluid stream as it passes through the nozzle aperture. However, the techniques used to form the nozzle aperture either require accurate machining of components on a microscopic scale, which is expensive and time consuming and does not give consistent results, leading to rejection of components during quality control assessment prior to use or to inconsistent operation of the device. Furthermore, the need to be capable of enduring the very high pressure surge, possibly as high as 600 bar, when the device is actuated requires the use of mechanically strong components. Again this adds to the cost of the device.
In PCT Application No GB91/02147 there has been described a form of construction which incorporates an integral one way valve and filter in the nozzle assembly to prevent air being sucked into the device through the discharge nozzle when the piston is being retracted to draw the metered dose of fluid from the reservoir and to prevent blockage of the fine nozzle aperture by solid particles entrained in the fluid. In a preferred form of such a construction a cylindrical plug is a push fit in a chamber immediately upstream of the nozzle orifice to provide an annular passage between the internal wall of the chamber and the radially outward wall of the plug. This annular passage has a radial dimension equal to or less than the nozzle aperture and thus provides a fine filter to remove solid particles which might otherwise block the nozzle aperture. The fine annular passage also imposes a flow restraint on the movement of fluid which is overcome by the high pressure generated when the piston is driven on its forward, or discharge, stroke to allow fluid to flow outwardly through the nozzle aperture. The flow restriction, however, prevents fluid from flowing back into the device as the piston is retracted. This reduces the risk of contamination of the fresh fluid drawn into the pressure chamber from the reservoir with air or fluid from the nozzle assembly downstream of the plug. Again such a device must be manufactured from metal to be able to withstand the pressure surge as the device is operated and thus requires high precision machining of components which is expensive.
An object of the invention, therefore, is to provide a device and a method for the manufacture of a nozzle which reduces the above problems and is capable of being made with a high degree of accuracy at low cost.
In accordance with one aspect of the invention, there is provided a nozzle with one or more nozzle outlets for the atomisation of fluids consisting of at least two plates which are connected together, possibly by an intermediate layer, wherein at least a, base plate has a grooved structure which connects the intake side of the nozzle to the nozzle outlet(s)
An embodiment of the invention can thus provide a nozzle (also referred to herein as a nozzle assembly) which is composed of two or more plates; at least one of which, a base plate, is formed with grooves which join an intake side and atomiser nozzle outlets provided on an oppositely disposed side, whilst another plate (the cover plate), which will normally be unstructured, is placed upon the structured side of the base plate and is joined firmly thereto. A nozzle assembly consisting of three layers can consist, for example, of a structured silicon plate, a flat silicon cover plate and a thin glass plate therebetween. Of course the functions of the base and cover plates can be reversed with a structured cover plate overlying an unstructured base plate.
The cavities in the nozzle assembly are usually of rectangular cross-section. However, a large number of variations is possible if the nozzle assembly is manufactured by way of the method described hereinbelow and related methods known to those skilled in the art. By using different etching methods, it is also possible to produce base plates with grooves of other cross-sections if so desired.
If the cover plate is structured in addition to the base plate, then it is possible to obtain other cross-sections, e.g. cross-sections of approximately circular shape. When both the base plates and cover plates are structured, both plates are usually given identical structures. Other variations are possible if the base plate and cover plate are structured in different ways but adapted to cooperate with one another.
According to another aspect of the invention, there is provided a spray generating device comprising a nozzle assembly for forming the spray of droplets from a stream of fluid fed to it by a means for generating a flow of fluid which nozzle assembly comprises:
a. a first member having formed in a first face thereof one or more fluid inlet(s) adapted to feed fluid to one or more fluid outlet(s) located at an edge of the first member, the outlet(s) being configured so that a spray of droplets is formed by the fluid outlet(s) from a stream of fluid flowing through them;
b. a second member secured upon the said first face of the first member and adapted to co-operate with the first member to provide one or more conduits each adapted to connect a said fluid inlet in fluid flow communication with a said fluid outlet, preferably the said second member co-operates with one or more channels formed in the said first face of the said first member to define the walls of one or more fluid conduits connecting said fluid inlet(s) to said fluid outlet(s); and
c. means for connecting said fluid inlet(s) to said means for generating the flow of fluid.
It is preferred that the fluid flow conduits each incorporate one or more narrow bore portions which have transverse dimensions and a transverse cross-section which is less than that of the fluid outlet(s) and which act as filters to protect the outlet(s) against blockage by solid particles in the fluid. The narrow bore portions also provide a flow restriction in the conduits which act as one way valves of the type described in PCT Application No GB 91/02147.
Preferably the first member is a substantially planar member and the channel(s), fluid inlet(s) and fluid outlet(s) are formed in a face of said first member with the longitudinal axes of the channel(s) and of the inlet(s) substantially parallel to the plane of said face and the plane of the outlet aperture substantially normal (perpendicular) to the plane of the first member; and the said second member is a second generally planar member which is preferably of substantially of the same planar shape and size as the first member.
The means for connecting the fluid conduits of said first member to the flow generating device is preferably provided by locating one or more of the fluid inlet(s) at an edge of the first or second members and providing means by which the first and/or second members can be mechanically connected to the flow generating device, for example by being a sealed push fit into the fluid outlet of the flow generating device. Alternatively, a third member can be provided which is secured to a second face of either the first or the second member and which is provided with a fluid conduit adapted to be put in fluid flow communication with the means for generating the fluid flow. For example the third member can carry a spigot which is a push or other fit in the outlet to a pump mechanism of the type described in PCT Application No GB91/00433 and which has a bore which communicates with the fluid inlet(s) in the first member. The bore of the spigot can act as the cylinder of the pump mechanism in such a device.
A nozzle assembly in accordance with the invention can readily be formed as a laminated unitary construction from components which have had the appropriate channels, inlets and outlets pre-formed therein by laser chemical etching photo-resist or other surface engraving techniques well known in the micro-forming art to achieve simple but accurately reproducible components having substantially flat opposing faces. These components can be secured together by diffusion bonding, adhesion, welding, clamping or other suitable techniques for securing them together in sealing engagement, optionally with sealing rings or other sealing interfaces between the members by simple assembly techniques.
In accordance with a further aspect of the invention, there is provided a nozzle assembly comprising:
a. a first member, which is preferably substantially planar, having one or more fluid inlet(s) formed therein, one or more fluid outlet(s) formed at an edge of the said first member and preferably also one or more channels formed in a first face of said first member substantially parallel to the plane of said face, the channel(s) connecting the fluid inlet(s) with the fluid outlet(s) in fluid flow communication and-preferably incorporating one or more narrow bore portions which are adapted to act as filters and one way valves;
b. a second member, which is preferably substantially planar and of substantially the same planar shape and size as the said first member, located upon said first face of said first member and co-operating with said first member to provide, and/or to define with the said channel(s) where present in said first member conduit(s) for connecting said fluid inlet(s) with said fluid outlet(s) in fluid flow communication; and
c. means for connecting the fluid inlet(s) of said first member in fluid flow communication with a means for generating the fluid flow.
Preferably, the fluid inlets, the fluid outlets and the connecting channels are formed wholly in the first face of the first member and the second member is a cover member secured over said first face to provide the wall forming the conduits. However, the second member can be provided with part or all of the connecting conduits as when the second member is provided with the channels and the first member provides the closing wall for those channels. Similarly, the second member can be provided with part of the inlets and/or outlets formed therein. For example, the first and second members can have mirror image halves of the inlets, outlets and conduits cut in the opposed faces thereof whereby securing them together forms the desired whole inlets, outlets and conduits.
For convenience, the invention will be described hereinafter in terms of a first member which has the whole depth of the inlets, outlets and channels formed in the first face thereof and the second member has a substantially flat face which provides a wall to complete the inlets, outlets and conduits.
The fluid outlet(s) act as the spray generating means of the nozzle assembly. These can therefore be simple fine bore orifices which can have rough, polygonal or other cross-sections or edges, as described in PCT Application No GB 91/02145, to form a spray of droplets from a stream of fluid passing through the outlet aperture. Thus, the aperture can have a triangular, squared or other regular or irregular polygonal shape, preferably having a maximum to minimum aperture dimension of from 1:1 to 10:1. The lip of the aperture can be rough, as when the aperture is formed by an electro-sputter erosion technique in which material is removed from the first member by striking an arc between the member and an electrode. However, it is preferred that the aperture have a sharp lip thereto over which the fluid flow changes direction sharply to achieve the secondary flow in the mainstream of the fluid flow. Typically the change in direction will be equivalent to at least 5%, preferably from 10 to 30%, of the total flow changing direction through 90xc2x0. Preferably, the change in direction occurs sharply, notably within an axial distance of less than five, preferably less than one, diameters of the width of the flow. Such change in direction, or secondary flow, can also be achieved by forming the aperture with an axially inwardly directed lip as opposed to an externally directed lip, for example where the aperture diverges along the line of flow and has an equilateral triangular plan shape with its apex directed against the intended line of flow of the fluid through the aperture. Alternatively, two channels can intersect within the plan area of the first member to form a turbulent flow in a single channel leading to the fluid outlet aperture located at the edge of the first member.
Alternatively, the change in direction can be caused by forming a flap or partial obstruction to the aperture whereby at least part of the flow of fluid through the aperture is subjected to a sharp change in direction by the flap or obstruction. Such a flap or obstruction acts on from 10 to 80% of the effective cross-section of the flow. Other forms of secondary flow generators are described in PCT Application No GB 91/02145 and the subject matter of that application is incorporated herein by this reference.
Where the fluid outlet is formed so as to generate the spray by means of the secondary flow caused by the shape and configuration of the outlet, we have found that satisfactory sprays can be produced with flow generating devices which generate a pressure low as 25 bar where comparatively large droplets are required, for example from 30 to 150 micrometres mass median droplet size. However, when droplets with a mass median size of less than about 20 micrometres are required, it will usually be necessary to use a flow generating device which generates a pressure of at least 50 bar, typically 100 to 400 bar.
The droplet size will also be affected by the nozzle aperture size. Thus, in general we have found that it is desirable to use apertures with maximum transverse dimensions of less than 500 micrometres, for example 50 micrometres or less. Where fine droplet sized sprays are required, the maximum transverse aperture dimension is preferably less than 30 micrometres. Such dimensions correspond to cross-sectional areas of from 5 to 2,500, eg. 10 to 500, square micrometres. Where coarse sprays are required, the aperture size can be to 100 micrometres maximum transverse dimension
As indicated above, the desired spray can also be formed by causing two or more jets of fluid to impinge upon one another or for a single jet, to impinge on a fixed impinger. In this case it is not necessary that the nozzle aperture cause any significant amount of secondary flow and a smooth lipped substantially circular, squared or rectangular aperture can be used. In order to produce an acceptable jet, it is preferred to use a flow generating device which generates a fluid pressure of from 50 to 400 bar and an aperture with a maximum transverse dimension of from 5 to 100 micrometres. Where two impinging jets are used, it is preferred that the line of flight of the jets include an angle of from 60 to 150xc2x0, preferably about 90 to 120xc2x0, at the point of impact and that the impact occur from 25 to 500, eg. from 30 to 100, micrometres from the plane of the edge of the first member at which the fluid outlets are located. Where a jet of fluid strikes a fixed impinger, it is preferred that this be located in the line of flight of the jet at a point before the jet begins to break up into separate droplets, typically less than 1000 micrometres downstream of the fluid outlet and that the surface of the impinger be angled to the line of flight of the jet so that the impinger is self cleaning and does not retain a significant amount of fluid thereon. A suitable form of such a self cleaning impinger is described in PCT Application No CB 92/0668.
Embodiments of the invention are described hereinafter in terms of the use of two fluid outlets to form twin jets of fluid which impinge upon one another to form a spray of droplets.
The fluid outlets are fed with fluid under pressure from the fluid flow generating means via the fluid inlet and the conduits formed in the first member. The fluid inlet is conveniently provided by a simple circular or other shaped chamber in the first member which is in direct fluid flow communication with the flow generating device via inlets at the edge of the first member or via a spigot or other means by which the nozzle assembly is mounted on the flow generating device. As indicated above, this spigot can form part of the pump mechanism of the flow generating device and an be carried by a third planar member which is mounted on the opposed face of the first member to that carrying the second member However, the first member could be formed with the spigot formed integrally therewith, for example as a metal or other tubular projection from the second face of the member.
Embodiments of the invention will also be described hereinafter where a third member carries the spigot protruding therefrom.
A single fluid inlet chamber in the first member typically receives all the fluid fed to the nozzle assembly and distributes it to the fluid outlet(s). If desired, the fluid inlet chamber can be elongated in one or more directions to assist uniform flow of the fluid to the fluid outlets. For convenience, the invention will be described hereinafter in terms of a single generally circular inlet chamber.
The inlet feeds fluid via one or more conduits to the fluid outlet(s). As stated above, these conduits are formed by etching, engraving or otherwise forming suitable channels in the face of the first member, for example by inserting fine wires or ablatable material filaments into the interface between the first and second members so as to form depressions in the opposed faces of the members and then removing or burning away the wires or filaments to form the channels and outlets. The channels will typically have a generally squared cross-section since they are in general formed by the removal of material uniformly across the whole width of the channel.
As stated above, it is particularly preferred than the channels have one or more portions which are narrower than the aperture of the fluid outlet so that these portions act as filters to prevent solid particles which might block the fluid outlets from reaching the outlet in a manner similar to the fine bore passages described in PCT Application No GB 91/02147. Such a fine bore portion of the conduit preferably has cross-sectional dimensions which are from 10 to 80% of those of the fluid outlet. It is also preferred that the fine bore portion of the channel cause a pressure drop of from at least 0.5 bar in the flow of fluid through the portion of the channel so that the narrow bore portion inhibits withdrawal of fluid from the channel during retraction of any pump mechanism used to generate the flow of fluid through the nozzle assembly. Preferably, the pressure drop is the minimum required to prevent return flow of fluid and air from the nozzle to the flow generating device and yet does not deleteriously affect free flow of the pressurised fluid through the channels and the fluid outlet(s). The optimum flow restriction can readily be determined for any given case, but will usually achieve a pressure drop of from 1 to 3 bar or more.
While the channels may communicate directly with a fluid outlet, it is preferred that the narrow bore portions of the channels be located between the fluid inlet and a plenum chamber which feeds fluid to the fluid outlets. Such a plenum chamber aids uniform distribution of the flow of the fluid to the outlets where more than one outlet is used, for example where two outlets are used to form two jets of fluid which impinge upon one another. The plenum chamber may also be configured so as to assist the formation of secondary flow in the fluid as it flows to the outlet(s), for example by incorporating curves or other wall configurations for causing swirling in the fluid flow.
The nozzle assembly finds use on a wide range of fluid flow generating devices, such as pressurised gas or aerosol type dispensers in which fluid is caused to flow out of a container by the expansion of a propellant gas. However, the nozzle assembly is of especial application in forming a spray from a flow of fluid generated by a manually operated pump mechanism, thus avoiding the use of a propellant gas. The pump mechanism may be of the type described in PCT Application NO GB 91/00433. The nozzle assembly is mounted by any suitable means upon the outlet from the pressure chamber of the pump, for example by a screw, bayonet, push or other fit, and receives the metered dose of the fluid when the spring or other energy source is released and the pressure within the pressure chamber rises. Other forms of fluid flow generator may also be used, provided that they can achieve the required pressure rise to discharge the fluid through the fluid outlet(s) as a spray with the desired mass median droplet size.
As indicated above, the channels, the fluid inlet the plenum chamber and the fluid outlets are all formed in one face of the first member, although the fluid inlet can extend through the thickness of the first member to communicate with the fluid flow generating means. Such a design readily lends itself to fabrication by selectively removing the necessary material from the required areas of the surface of the first member by etching or engraving techniques which can be accurately controlled to form the very fine features required for the present invention. Such techniques are known and used in the formation of channels and nozzle outlets in the manufacture of ink jet printer heads, see for example US Patent 4915718 and European Application No 0397441, and in general comprise the application of a mask to a photo-resist or chemically etchable material; sensitizing the material and removing the material in the required areas by application of a suitable etching material. Alternatively, the channels can be formed by burning away the material using a laser or by striking an arc between the member and an electrode. Other methods for forming the features on the surface of the first member may be used for example milling or fine engraving of silicon, ceramic or metal plates.
Such techniques can be used to remove accurately controlled amounts of material from accurately defined selective areas of the surface of the first member to form, within reason, any desired shape of channel, fluid outlet or other feature. Such techniques are especially applicable to planar surfaces and it is therefore preferred that the surface of the first member in which the features are to be formed is substantially flat. However, they may also be applied to curved or irregular surfaces so that the surface of the first member need not be flat if desired.
The components of the nozzle assembly for use in the present invention thus readily lend themselves to manufacture by such techniques from a wide range of materials which are conventionally used in such techniques, for example photo-resist plastic, silicon, ceramics, metals. Such materials can be produced to a high degree of accuracy and are often strong enough to resist the stresses due to the high pressure rises imposed upon the nozzle assemblies without the need for supporting framework or other structures. Furthermore, being substantially flat members the first, second and third members can readily be secured to one another in sealing engagement. Thus, metal, silicon or ceramic plates can readily be bonded together by pressure welding or by diffusion bonding in which an interface of a suitable metal, for example gold, is located between the opposed faces of the member and bonding caused by the application of heat and pressure. Such diffusion bonding has the advantage that little distortion of the shape of the channels and other features in the face of the first member is caused, thus preserving the accuracy of the features once formed.
Alternatively, the first and second members of the nozzle assembly can be secured in position by the use of adhesives, conventional ultra-sonic or other welding techniques or by mechanically clamping the components together. If desired, sealing rings or gaskets can be located between the opposing faces to ensure a fluid tight seal. However, where the faces of the members are sufficiently flat, this will usually not be necessary and the adhesive or metal diffusion interface between the opposed faces will ensure an adequate seal.
If desired, the assembled nozzle assembly can be located within a supporting housing or the like to impart the necessary strength to the assembly to withstand the high pressures generated by the devices of our PCT Application NO GB91/00433.
In particular, the nozzle assemblies according to the invention are preferably manufactured by means of the following steps:
structuring a batch of base plates with grooves;
joining the base plates and cover plates; and
separating the individual nozzle assemblies. The
grooved finish is preferably produced simultaneously for a plurality of nozzle assemblies over a large surface area in a parallel manufacturing process, and then the base and cover plates are joined in one step (i.e. a batch process). Thereafter, the composite structure is divided into individual tiles or chips, and the inlet and outlet openings of the nozzle assemblies are opened up.
There are special advantages with this type of manufacture. The batch manufacture first of all makes it possible to produce individual component parts which are particularly cheap, and which could only be produced using serial processing methods at considerably greater expense. The batch manufacture secondly guarantees a specific constant quality for all parts which can be reproduced repeatedly under the same processing conditions, a quality which is never subject to gradual change, as would be the case in serial processing methods due to wear of the worktool(s).
Also, the position and placement of the parts in the process are determined likewise by the overall design, and does not therefore have to be altered by time-consuming sorting- or handling machines.
Thus, the present invention relates to new, highly effective nozzle assemblies and methods which can be used to produce large numbers of these nozzle assemblies so that they are of constant high quality; in addition, a filterxe2x80x94possibly a multi-staged filter can be integrated in the nozzle assembly.
The materials and methods which can be used according to the invention produce nozzles which excel through a number of advantages:
high mechanical stability;
a high degree of resistance to chemical influences (e.g. aqueous medicine solutions, acids);
low surface roughness of the grooves;
low influence of larger pressure- and temperature differences;
valve function of the nozzle members filled with fluid with lower pressures.
The nozzle assemblies according to the invention can be very small in size, so that the dead volume is very small, and therefore when the nozzle members are used in the therapeutic domain (production of inhalation aerosols) the dead volume accounts for only a small fraction of the quantity of fluid to be diffuse.
Surprisingly, the provision of shallow grooves means that no problems result with transportation of the fluid, despite the fact that small flow cross-sections are likely to give problems with the boundary layers.
The nozzle assembly of the invention thus offers a simplified design which does not required expensive and time consuming machining of components and which enables components to be made reproducibly to a high degree of accuracy and which can readily be assembled to form the nozzle assembly.
The invention also provides a method for producing a nozzle assembly for use in a spray generating device of the invention, wherein the fluid outlet(s), the fluid inlet(s) and the connecting channels are formed in the face of the first member by selectively removing material from that face; and securing a second member upon the said first member whereby the face of said second member opposed to said first member co-operates with the said fluid outlet(s), fluid inlet(s) and said channels to form the fluid flow paths for said nozzle assembly.